The present invention relates to a braking-power booster including means for suppressing noise during use of the booster.
Braking-power boosters are known, for instance, from Federal Republic of Germany published application OS 34 24 410 corresponding to U.S. application Ser. No. 747,403, filed July 2, 1985. It has been found in practice that such braking-power boosters operate well. But, as a result of the immediate response of the valve upon pressure equalization, the braking-power boosters have the disadvantage that high velocities of liquid flow occur at the sealing edge of the valve seat against the plate of the valve. This produces disturbing noises from the booster. At the end of the braking process particularly, a hissing, sucking noise occurs because the atmospheric air previously present in the right pressure chamber flows with high velocity over the sealing edge into the left chamber in which there is a vacuum. The time period which the braking-power booster requires to come into its starting position should not be longer than 0.2 seconds. As a result, measures to reduce the velocity of air flow by opening the valve more slowly cannot be permitted. An object, for example a disk of porous material, like foam rubber, arranged in the flow path mitigates the development of noise occurring upon air flow. On the other hand, it considerably lengthens the reset time of the booster. Furthermore, parts of the foam rubber disk have been drawn into the sealing seat and have thus led to disturbances in operation.